Malignant: Malignant neoplasms, or "cancers" are those whose natural history (i.e., behavior if untreated) is to cause the death of the patient. Malignancy is expressed by: 1. Local invasion, in which the neoplasm extends into vital organs and interferes with their function. 2. Metastasis, in which cells from the tumor seed out to other parts of the body and then grow into tumors themselves 3. Paraneoplastic syndromes, in which the neoplasm secretes metabolic poisons or inappropriately large amounts of hormones that cause problems with functions of various body systems.